The effect of hot calendering of the substrate on the barrier properties of poly(vinyl alcohol)-coated papers

The influence of the surface characteristics of the paper substrate on the possibility of coating the paper with a thin homogeneous polymer film has been investigated. Solutions of poly(vinyl alcohol), PVA, were used to coat two different paper grades on a pilot scale. Some of the paper specimens were calendered at high temperatures (>200 degreesC) since this is known to have a strong effect on the surface smoothness and surface porosity. The high-temperature calendering was found to improve the spreading of the polymer solution on the paper surface and led to an improvement in the homogeneity of the film at low applied coat weights. The better covering ability of the polymeric film seemed to be the main reason for the improved barrier properties compared to those of a coated but uncalendered substrate. The grease resistance, the air permeance and also the water vapour transmission rate were considered. The interaction between substrate and polymer solution is described and discussed in terms of contact angle measurements and sorption behaviour at short contact times. A partially hydrolysed PVA-grade provided a better coating result than a fully hydrolysed PVA. Carboxylating a fully hydrolysed PVA-grade enhanced the barrier properties especially with regard to water vapour transmission rate.